Design and Embodied Carbon Optimisation of a Composite Floor System with Thin Concrete Shells on a Beam Grid

Thin shell floors can reduce concrete consumption compared to conventional reinforced concrete flat slabs. Prefabrication of shell structures for longer spans may require segmentation, and previous studies have shown that the overall performance is highly sensitive to fabrication tolerance. As an alternative,
we propose a composite floor system that supports multiple individual shells on a steel beam grid. The novel system covers the total floor area between columns with a collection of several identical rectangular segments that are covered by separate shells, while the corners of the shells are supported by a grid of steel beams. For a given column grid, several variations of the proposed floor solution can be designed by dividing the total floor area into different numbers of equal sections, each to be designed as an individual shell. This paper presents the conceptualisation and preliminary structural design of the composite system with concrete shells and steel beams. For the same column spacing, the embodied carbon and floor height of three possible variations of the novel system are compared herein against two designs treated as benchmarks: a design with a single shell and a conventional flat slab design. As the span of the individual shells decreases, the embodied carbon attributed to concrete decreases. However, despite the increased number of beams needed for sectioning the total area into shells with shorter spans, variations in applied loads and loading points also affect the design of supporting beam grid. Therefore, relationship between the embodied carbon from the steel beams and the span of the individual shells is nonlinear, highlighting the importance of parametric optimisation. The proposed composite system can achieve embodied carbon reductions of up to 58% compared to a conventional flat slab, a level similar to that of a single-shell design but with almost one-third less floor height